1. Field of the Invention
The present disclosure relates to a molded case circuit breaker, and more particularly, to a stationary contact arm assembly for a molded case circuit breaker.
2. Description of the related art
A molded case circuit breaker is a power device having a protective function to switch a relatively low voltage power circuit under several hundred volts or trip a circuit when a fault current such as an over current or short-circuit current occurs on the circuit.
As is well known, a molded case circuit breaker may include a stationary contact arm, a movable contact arm having a closed position formed to be brought into contact with the stationary contact arm and an open position formed to be separated from the stationary contact arm so as to break an electrical circuit, a switching mechanism configured to provide a driving force for driving the movable contact arm to a closed or open position, a trip mechanism configured to sense a fault current when it occurs on the circuit so as to trigger the operation of the switching mechanism to the open position, an extinguishing mechanism installed around the movable contact arm and stationary contact arm to extinguish an arc occurring during the open position operation, an enclosure for accommodating the constituent elements, namely, an upper cover and a lower case, and the like.
The molded case circuit breaker may also include a molded case circuit breaker with a current limiting function for automatically limiting a fault current using an electromagnetic repulsive force generated between the contacts of the stationary contact arm and movable contact arm when the fault current occurs, and a molded case circuit breaker without the current liming function.
In order to perform such a current limiting function, the stationary contact arm should be a current limiting type stationary contact arm, and the current limiting type stationary contact arm with a terminal portion and a contact portion formed at both ends thereof has a laid down U-shaped geometric feature in which the contact portion is bent toward the side of the terminal portion.
Owing to the geometric feature, the direction of a current flowing into the contact portion and direction of a current flowing out of the contact portion are opposite to each other, and thus a magnetic field formed around the flowing-in current and flowing-out current are repulsive to each other, and in particular when a current flowing through the circuit is abnormally large, the corresponding magnetic repulsive force becomes large to the extent that the movable contact arm is pushed out in the direction of being separated from the stationary contact arm.
The present disclosure relates to the current limiting type stationary contact arm assembly in which the movable contact arm is separated from the stationary contact arm using a magnetic repulsive force, thereby automatically limiting an abnormal current on an electric circuit.
For such a current limiting type stationary contact arm assembly, there has been disclosed a technology in which a magnet assembly formed with a plurality of steel plates is attached to the stationary contact arm to more greatly generate an electromagnetic repulsive force for the current limiting function, thereby enhancing the magnetic permeability of the stationary contact arm.
However, during the switching operation between the movable contact arm and stationary contact arm of the molded case circuit breaker or subsequent to the current limiting operation, it is required to maintain the position of the magnet assembly formed with a plurality of steel plates in a stationary manner even with repeated shocks while the movable contact arm is returned again to a position in contact with the stationary contact arm.
In positionally fixing the magnet assembly to the stationary contact arm, a method of fastening the magnet assembly with the stationary contact arm using a retaining screw has been used in the related art.
However, the related art in which the magnetic assembly and the stationary contact arm are fastened with a retaining screw further requires a retaining screw and accompanies the process of fastening the corresponding retaining screw, thereby causing a problem of increasing the cost of the molded case circuit breaker and reducing the productivity.